| ⊦ reachable-n(H, n + 1, r, r0) ∧ n < n + 1, reachable-n(H, n + 1, r, r0) ↔ (∃ r1. reachable-n(H, n, r, r1) ∧ reachable-1(H, r1, r0)) |
reachable-n(H, n + 1, r, r0) ⊦ ∃ r1. reachable-n(H, n, r, r1) ∧ reachable-1(H, r1, r0), reachable-n(H, n + 1, r, r0) ∧ n < n + 1
∃ r1. reachable-n(H, n, r, r1) ∧ reachable-1(H, r1, r0) ⊦ reachable-n(H, n + 1, r, r0), reachable-n(H, n + 1, r, r0) ∧ n < n + 1